Gravity Emerges from Quantum Information, Say Physicists

[Geriatrix]

http://www.technologyreview.com/blog/arxiv/24975/

One of the hottest new ideas in physics is that gravity is an emergent phenomena; that it somehow arises from the complex interaction of simpler things.

A few month's ago, Erik Verlinde at the the University of Amsterdam put forward one such idea which has taken the world of physics by storm. Verlinde suggested that gravity is merely a manifestation of entropy in the Universe. His idea is based on the second law of thermodynamics, that entropy always increases over time. It suggests that differences in entropy between parts of the Universe generates a force that redistributes matter in a way that maximises entropy. This is the force we call gravity.

What's exciting about the approach is that it dramatically simplifies the theoretical scaffolding that supports modern physics. And while it has its limitations--for example, it generates Newton's laws of gravity rather than Einstein's--it has some advantages too, such as the ability to account for the magnitude of dark energy which conventional theories of gravity struggle with.

But perhaps the most powerful idea to emerge from Verlinde's approach is that gravity is essentially a phenomenon of information.

Today, this idea gets a useful boost from Jae-Weon Lee at Jungwon University in South Korea and a couple of buddies. They use the idea of quantum information to derive a theory of gravity and they do it taking a slightly different tack to Verlinde.

At the heart of their idea is the tricky question of what happens to information when it enters a black hole. Physicists have puzzled over this for decades with little consensus. But one thing they agree on is Landauer's principle: that erasing a bit of quantum information always increases the entropy of the Universe by a certain small amount and requires a specific amount of energy.

Jae-Weon and co assume that this erasure process must occur at the black hole horizon. And if so, spacetime must organise itself in a way that maximises entropy at these horizons. In other words, it generates a gravity-like force.

That's intriguing for several reasons. First, Jae-Weon and co assume the existence of spacetime and its geometry and simply ask what form it must take if information is being erased at horizons in this way.

It also relates gravity to quantum information for the first time. Over recent years many results in quantum mechanics have pointed to the increasingly important role that information appears to play in the Universe.

Some physicists are convinced that the properties of information do not come from the behaviour of information carriers such as photons and electrons but the other way round. They think that information itself is the ghostly bedrock on which our universe is built.

Gravity has always been a fly in this ointment. But the growing realisation that information plays a fundamental role here too, could open the way to the kind of unification between the quantum mechanics and relativity that physicists have dreamed of.

 

[plazma]

Interesting, but basically just more quantum gobblydegook.

We still don't know what gravitation is, or even why matter has mass. Every week there is a new Einstein wannabe with a new theory to explain why matter attracts other matter.

For me the interesting thing about gravitation is how the lines between physics and philosophy become blurred when you discuss gravity.

 

[scotty777]

lol, gravity is just a bitch. Like no one actually knows what it is, but everyone has been doing very well in describing what it does...

But what happened to string theory? I thought that was the mystical and amazing theory that described how everything in the universe related to each other. (Also, I heard the maths behind string theory is too crazy to punch into a computer, so you have to solve it the old fashioned way)

 

[Picard]

This makes me think of the movie The Matrix where the people are plugged into a computer and where information is creating the physical universe around these people.

 

[Geriatrix]

Um, I'm thinking you guys don't really understand the concepts and terms in this article. Anyway, its not just some dude sipping a cup of java shooting philosophy from the hip. There's some solid math and ground work behind this theory(the scientific version, not the tea room version).

Anyway, lets see what his peers make of it. Strange that it points to Newtons ideas though and not Einstein.

 

[Happy Camper]

Um, I'm thinking you guys don't really understand the concepts and terms in this article. Anyway, its not just some dude sipping a cup of java shooting philosophy from the hip. There's some solid math and ground work behind this theory(the scientific version, not the tea room version).

Anyway, lets see what his peers make of it. Strange that it points to Newtons ideas though and not Einstein.

Of course it would point to newton and not einstein, newton was concerned with Macro mass (gravity) while einstein was more concerned with micro (quantum, less or no gravity at all).

 

[Devill]

Um, I'm thinking you guys don't really understand the concepts and terms in this article. Anyway, its not just some dude sipping a cup of java shooting philosophy from the hip. There's some solid math and ground work behind this theory(the scientific version, not the tea room version).

Anyway, lets see what his peers make of it. Strange that it points to Newtons ideas though and not Einstein.

I would just love to be able to understand that maths (not just the basics of it but the real mechanics behind it)

I agree with you that it is pretty surprising that it points to Newton's theories and not Einstein's.

 

[Moederloos]

Nonsense - if gravity was created by information, Luthuli House would be floating.

:grin:

But, on a more serious note: sounds interesting. The universe is probably a lot more bizarre than we think.

 

[Devill]

Nonsense - if gravity was created by information, Luthuli House would be floating.

:grin:

But, on a more serious note: sounds interesting. The universe is probably a lot more bizarre than we think.

ROFL

And I have to agree that I think the universe will reveal some weird and wonderful secrets yet... I just hope I am not dead by that time

 

[Geriatrix]

ROFL

And I have to agree that I think the universe will reveal some weird and wonderful secrets yet... I just hope I am not dead by that time

Hey at least you exist now and not 300 years ago. You get to see the development of cutting edge of gravitational theory. If you lived 300 years from now this would all be boring and obvious history.

 

[Devill]

Hey at least you exist now and not 300 years ago. You get to see the development of cutting edge of gravitational theory. If you lived 300 years from now this would all be boring and obvious history.

Or the accepted theories of today might be looked back on in 300 years and be remembered as "The-stupid-things-people-actually-believed"

 

[Geriatrix]

Science works in mysterious ways.

 

[plazma]

Um, I'm thinking you guys don't really understand the concepts and terms in this article. Anyway, its not just some dude sipping a cup of java shooting philosophy from the hip. There's some solid math and ground work behind this theory(the scientific version, not the tea room version).

Anyway, lets see what his peers make of it. Strange that it points to Newtons ideas though and not Einstein.

Ummm.. the reason why some of us read the post in the first place is exactly because we do understand all of it, and actually have an interest in the topic, and have read a few books about - gravitation, or studied it at university. Ad hominem stuff is not considered scientific.

 

[Palimino]

Strange that it points to Newtons ideas though and not Einstein.

Quantum mechanics was too weird for Einstein.

Trivia
Einstein was a religious man. A famous saying when confronted with quantum mechanics – “God does not play dice with the Universe”.

 

[The Philosopher]

PALIMONO, HE WAS VAGUELY RELIGIOUS, i think it was taken out of context

 

[Geriatrix]

More:
http://www.fqxi.org/community/articles/display/132

When thieves stole Erik Verlinde’s laptop and keys, while he was holidaying in the south of France, they could have had little notion that their crime would lead to a new model for gravity. But forced into taking an extra week’s vacation time, Verlinde began to ponder whether gravity might not be a fundamental force of nature, arising instead from thermodynamics. His ideas could give the controversial loop quantum gravity theory—in which spacetime is made up of quantum threads—a boost, and help explain the accelerated expansion of the universe.

Gravity may be the force that we are most familiar with in everyday life, but physicists do not yet understand its origin. Newton told us that apples fall towards Earth with an acceleration that depends on the Earth’s mass, the apple’s mass, and its distance from the centre of the Earth, while Einstein described gravity by the warping of the fabric of spacetime. But while these theories describe how gravity works, they don’t explain how it arises.

Verlinde, a string theorist at the University of Amsterdam in the Netherlands, believes that the key to understanding gravity is "information." He was inspired by early work on information storage in black holes by Stephen Hawking and Nobel laureate Gerard ’t Hooft. "When I was about fifteen I saw them on television talking about the physics of elementary particles and black holes," says Verlinde. "I knew then that I wanted to work in that area."

The Television Event Horizon

Hawing and ’t Hooft had both worked on the so-called holographic principle, which relates the information content—or entropy—of a black hole to the surface area of its event horizon, the hypothetical sphere around the black hole where gravity becomes so strong even light can’t escape. It’s as if the horizon is a spherical television screen with all the information about the three-dimensional volume within encoded on the pixels on its surface. Verlinde has shown that by combining the holographic principle with the thermodynamic quantities of heat and mechanical work, it’s relatively straightforward to derive Newton’s classical equation of gravity.

The work has been causing a stir amongst physicists. "Verlinde’s paper is remarkable in that we all felt so stupid for not having seen it before," says FQXi’s Lee Smolin of the Perimeter Institute, Ontario. "The mathematics involved is just high school algebra."

It might sound like re-inventing the wheel, but the approach implies that gravity is nothing more than the result of a system maximising its entropy, or disorder. At first glance, this looks like bad news for the quantum gravity crowd. If gravity is an "entropic force," there is no longer a need for physicists to attempt to reconcile general relativity with quantum mechanics, or hunt for the hypothetical graviton (the particle posited to carry the gravitational force just as photons mediate the electromagnetic force), says Paul Frampton, at the University of Tokyo in Japan. Rather, all we need to explain the interactions of particles is the Standard Model of particle physics and entropy. "It means that everyone looking into quantum gravity is misguided," says Frampton.

Quantum Threads

However, not all gravity researchers take that view. Smolin, a long term proponent of loop quantum gravity (LQG), believes that Verlinde’s work is not only compatible with LQG, it could even help to explain how familiar Newtonian gravity might emerge in this picture. According to LQG, spacetime isn’t the smooth fabric that Einstein envisioned; rather, if you zoom down to scales of 10-33 cm, the fabric turns out to be woven from quantum threads. The key point for Smolin is that the holographic principle is also valid in this framework, allowing him to apply a version of Verlinde’s argument to demonstrate directly for the first time that loop quantum gravity has a limit that yields Newtonian gravity.

Smolin notes that Verlinde’s model is tied to earlier work by FQXi member Ted Jacobson, who had shown in 1995 that Einstein’s equations of general relativity could be derived using thermodynamics and the holographic principle. "The wonderful thing about the arguments of Jacobson and Verlinde is they give a deep reason for why a quantum theory of gravity should yield the phenomena of gravitation," Smolin writes in his recent paper

Frampton and colleagues Damien Easson and Nobel Laureate George Smoot have been looking at possible observable consequences of Verlinde’s entropic force. So far, cosmologists have struggled to explain why the expansion of the universe is accelerating using just standard general relativity. Instead, they attribute the acceleration to some mysterious "dark energy." To find an possible alternative to dark energy, Smoot’s team considered a spherical screen that lies on the apparent horizon of the universe, where distant objects recede at the speed of light. As information is sucked out across the horizon, the area of the screen grows, which, according to the holographic principle, increases the entropy of the universe. This gives rise to an entropic force that could explain the acceleration, "derived as a response to various microscopic fundamental forces such as electromagnetism," says Easson, at Arizona State University, Tempe. However, Easson adds that the work is "extremely speculative" at this stage (arXiv:1002.4278v2).

If such derivations of dark energy stand up then Verlinde’s ideas "could in some sense complete general relativity," says physicist Sabine Hossenfelder at the Nordic Institute of Theoretical Physics in Sweden. However, there is still a long way to go before physicists will abandon the notion that gravity is a real force as there are several things that remain vague in Verlinde’s formulation, she adds.

Frampton, however, is convinced that Verlinde is on the right track. "I believe that gravity is entirely explained by increases in entropy; there isn’t a fundamental gravitational interaction," he says. "That’s the bottom line. Is that crazy enough?"

 

[Happy Camper]

Interesting stuff Geriatrix, actually blows my mind! Thnx ++